A piano bench is a rectangular seat for piano playing, and often has a compartment under the seat for music or whatever. A piano stool is a different sort of seat, circular in form and a little smaller. The seat height is often adjustable by spinning the seat (which is mounted using a large screw mechanism in such cases).

Thanks, Drew, for the definition, but have you seen anyone use a stool at a piano? That's why I put it in green; it's not wrong; it just doesn't sit right --- with me. Even "sales room," which I liked for its cleverness, is rarely if ever used. I see that I should not have used "same here" under the question icon since Teton range seems made up while piano stool exists but is a rarity.

Piano stools are definitely rare these days; no argument at all there. I think maybe the last time I've seen one used was in accompanying a typical elementary school music program...back when I was in elementary school in a small town. There's a reasonable chance they may still be in use there, assuming I'm remembering things straight. The town hall there has seen little change, either before or since.

I do kind of hope they'll come back some day, though, as an adjustable stool is nicer to use than a non-adjustable bench IMHO.